Do you think we'll see one before the end of the year for the earliest one?

DLC is always pretty much set for its existence.

Wait until ME3

Humm ...
Find out the release date for Mass Effect 3 and then subtract 1 or 2 month.

I think it will be a year after the game shipped, at the earliest. I don't think the smaller stuff, like weapon packs, will ever drop.

 I'm just praying for it to happen. Now that I've finished all of my main quests, I'm running out of anomalous side missions, so I'll have to get Kasumi and Overlord sometime (and the Aegis Pack, cause the Kestrel Armor just looks amazing). 
Definitely getting Lair of the Shadow Broker as soon as it's released, though.     

Not for a while.  Whenever there is multiple DLCs, I try to hold out for picking up a GOTY edition on the cheap with all the stuff.

2-3 months for Kasumi I guess, maybe 5 or so for Overlord. Both DLC are decent though, worth the 560 points.

The DLC for ME1 I believe didn't go on sale until a week to two weeks before ME2 was released. My guess it'll be the same with this one.

There seems to be about two different ways that DLC goes: They never get any cheaper or they become free after a couple of years. The latter however only seems to occur with multiplayer map packs for older games that have a major sequel and everyone flees the original. I'm going to lean towards Mass Effect 2s DLC never getting any cheaper.

I'm sure it will be a deal of the week down the line but you will have to make sure you don't miss that week.